1. Field of the Invention
The present invention relates to a plasma processing method and plasma processing device for fabricating semiconductor devices, and more particularly to a plasma processing method and plasma processing device for ashing in a preprocess of wafer processing.
2. Description of the Related Art
Currently such a technology as ESC (Electro-Static Chack) is being used for ashing, which tends to jump up equipment cost. And since high throughput is demanded, a 2000 W or higher microwave is sometimes used to increase the ashing speed. Also Cu is more frequently used for the wiring of semiconductor devices, and decreasing the temperature of ashing is demanded more to prevent the oxidation of Cu. For example, conventionally ashing is performed in a 200° C. or higher stage temperature area, but now it is required to be performed in a 100° C. or less temperature area to use Cu. In a low temperature area, the ashing speed tends to drop, so the power of the microwave must be increased to increase the ashing speed.
Generally in a plasma processing device, which performs the etching and ashing (hereafter simply called ashing), the inner face of the wafer processing chamber is damaged by being exposed to plasma, and particles are generated. In some recent cases ashing is performed with adding fluorine gas to O2 plasma (e.g. see Japanese Patent Application Laid-Open No. 2000-12521) where the wafer processing chamber is easily damaged. Therefore it is proposed to use alumite for parts of the chamber so as to prevent the generation of particles (e.g. see Japanese Patent Application Laid-Open No. H10-50663).
However even if the inner face of the wafer processing chamber are coated with alumite, the alumite coating itself is damaged by being continuously exposed to plasma, where aluminum on the under-layer is exposed to plasma, and particles are generated. O radicals in the plasma collide with the alumite coating and causes cracks, opens generated cracks and causes the stripping of the exposed aluminum under-layer and the alumite coating.
If ashing is performed by adding fluorine gas to O2 plasma, the damage of alumite coating tends to progress even more easily. In the case of a wafer processing chamber that is used in a high microwave area, the energy of the O radicals increases and damage increases particularly in a high plasma density area. Also in the case of a surface wave plasma type wafer processing chamber, the plasma density increases and damage increases in the upper area of the chamber.
The resist on the wafer, for which ashing is performed, is comprised of such elements as carbon (C) and hydrogen (H), so during ashing the deposit components such as C and H are supplied from the resist to the plasma, and are deposited onto the inner face of the wafer processing chamber to protect it from plasma. However when the resist decreases as ashing progresses, the supply of the deposit components to the plasma decreases, the deposit amount on the inner face of the wafer processing chamber decreases, the wafer processing chamber is damaged, and particles are generated.
In the fabrication of semiconductor devices, particles are one of the major obstruction factors which drop yield, so the prevention of particle generation remains a problems.